In the continuous casting of molten metals such as steel, molten metal is poured from a ladle into a continuous casting mould via an intermediate vessel called a tundish which acts as a constant head reservoir. The tundish has a metal floor, sidewalls, and one or more outlets set in the floor or sidewall. To protect the metal floor and sidewalls from the molten metal, it is usual to line the floor and sidewalls of the tundish with a relatively permanent lining, often made of bricks or a castable. The tundish additionally may be provided with an inner, expendable lining of refractory. For example, see British patent No. 1,364,665.
While it is desirable for the expendable lining to be highly heat-insulating, it is also desirable for the expendable lining to have substantial resistance to erosion and corrosion by molten metal and slag. However, any change in the lining that improves its heat-insulating properties is usually associated with reduced density which tends to lessen erosion/corrosion resistance.
Various proposals have been made for expendable linings. For example, U.S. Pat. No. 5,139,239 shows forming an expendable lining in a molten metal handling vessel that has an outer metal casing lined with a permanent lining. Portions of the surface of the permanent lining are covered with a removable material. A slurry of refractory material is applied over both the removable material and the remaining exposed portions of the permanent lining. The slurry of refractory material can be applied by spraying, although gunning or trowelling may be used. The removable material may be in the form of consumable material, for example cardboard, strawboard, fiberboard or polystyrene. Alternatively, the removable material may be in the form of a consumable cellular material, e.g. polyurethane foam. The slurry is dried to form the expendable lining.
Traditional expendable liner materials as described above have employed combustible fillers to reduce the density of the formed expendable lining. These filler materials may be organic, inorganic, or synthetic fibers or spheres. The drawbacks to using fillers to reduce the density of the lining material are that the amount of density reduction is limited to the amount of filler added. Also, the temperature required to remove any combustible filler materials can generate undesirable stress in the lining as the combustible materials are oxidized. The filler also can reduce the strength and chemical durability of the resulting lining, and produce undesirable interconnected porosity. The filler can also increase water requirements, thereby necessitating extra drying time and expense, and as well increasing the risk of shrinkage cracking. In addition, the filler may cause handling and flow difficulties.
U.S. Pat. No. 5,188,794 shows a lining obtained by application of burnt dolomite in the form of grains mixed with an organic binder such as a thermosetting resin. After application of the lining material, it is heated to decompose the carbonate and/or the binder of the composition to provide a porous layer.
Although the methods of the art have provided porous materials which are useful as expendable linings such as on vertical surfaces, these methods have required high temperatures to produce a porous lining. Also, these methods often yield undesirable interconnected porosity. A need therefore exists for expendable linings which can be formed without the high temperature requirements of the art, and which avoid interconnected porosity.